I have used Rock Auto extensively over the years for all of my vintage cars, and I've mostly had good experience and received quality parts. Their system, which lets the customer see all the MFR's of parts available for whatever you're looking for, makes it a handy research tool, like others here have said.
I also like to shop locally. Often I need 'auto parts store therapy' and enjoy the browsing aspect.
One of the best stores out here is Winchester Auto, a small chain in the south bay and Sana Cruz area that's got a lot to look at. I have been in a few of the old time dirty parts stores they mention below and I can't wait to get out, haha....
Winchester Auto Parts
If you have ever had a chance to visit one of our 5 locations, you would have noticed something unique, quite different than other auto part stores. We are not a mass merchandiser or mega-chain auto store which specializes in oils and "mechanics in a pour can". On the other hand, we don't typify your standard old time mom and pop parts store with wooden shelves, front stools, and a 2 inch layer of dust covering the entire front of the store. We are a finely tuned blend of both, offering you large, clean, well lit, organized automotive stores, with extensive inventories.